A battery pack, e.g., a lithium-ion battery pack, lead-acid battery pack, or the like, usually includes a group of battery cells coupled in series. When the battery cells are charged to above an overcharge voltage, characteristics of the battery pack may be degraded and safety of the battery pack may be diminished. When the battery cells are unbalanced because one or more cells of the battery cells have cell voltages exceeding a balance threshold, performance of the battery pack may be affected. Therefore, there is a demand for a battery management system to manage the battery cells of the battery pack, to ensure adequate characteristics, safety and performance of the battery pack. As to the battery management system itself, high efficiency is desirable.